Calculate BMI, understand the result and prepare questions for your next visit. This tool is for adults aged 20 and older and offers a printable summary that can be saved as PDF. U.S. CDC categories are selected by default; Korean categories can be selected separately from the result language. The reference table in the article below uses CDC categories.
During pregnancy, with major fluid retention or ascites, or after limb loss, do not apply these adult BMI categories to the measured weight without individual assessment.
How to interpret the number
For adults aged 20 and older, CDC categories are below 18.5 (underweight), 18.5 to below 25 (healthy weight), 25 to below 30 (overweight), 30 to below 35 (obesity class 1), 35 to below 40 (class 2), and 40 or higher (class 3). These are U.S. CDC categories. Korean adult guidance uses 23 to below 25 as pre-obesity and 25 or higher as obesity; the same BMI can have a different category in Korea. Categories are assigned before the displayed BMI is rounded to one decimal place.
| BMI (kg/m²) | U.S. CDC category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to below 25 | Healthy weight |
| 25 to below 30 | Overweight |
| 30 to below 35 | Obesity, class 1 |
| 35 to below 40 | Obesity, class 2 |
| 40 or above | Obesity, class 3 |
Check your measurements before entering them
Enter height in centimetres without shoes and weight in kilograms. Type 170, not 1.70, for a height of 170 cm; the calculator converts to metres internally. A consistent measurement routine helps when comparing results over time. Its input limits of 80–250 cm and 20–500 kg are software checks for likely entry errors, not a claim that adult BMI categories are clinically suitable throughout those ranges.
Example and limitations
At 170 cm and 80 kg, BMI is 80 ÷ (1.70 × 1.70) ≈ 27.7 kg/m², which falls in the CDC overweight category. BMI is a screening measure. It does not measure body fat or establish a diagnosis; medical history, waist size, muscle mass and other findings can matter.
This adult category tool is for people aged 20 or older. Children and teens need an age- and sex-specific BMI-for-age assessment. Current weight during pregnancy is not assessed by these adult BMI categories; pre-pregnancy BMI and pregnancy stage matter. Significant oedema or ascites can add fluid weight, and limb loss changes the relationship between body weight and height. Seek individual assessment in those situations. BMI can also miss changes in muscle and fat in older adults or people with substantial muscle mass.
What BMI cannot tell you
BMI does not directly measure abdominal fat or distinguish fat from muscle. If clinically appropriate, measure your waist and use the waist-to-height ratio calculator alongside BMI. NICE recommends using both for adults with BMI below 35 as a practical way to assess central adiposity. Blood pressure, glucose results, history, and other findings may also matter.
The example BMI of 27.7 is overweight under the U.S. CDC adult categories but class 1 obesity under the Korean adult categories. The arithmetic is the same; the population-based cutoffs differ. Check which guidance your own clinician or health report uses.
What about weight-loss medication?
A BMI category alone does not decide medication eligibility. Product labelling, starting BMI, weight-related conditions and safety considerations vary by country and treatment. See who may qualify for GLP-1 medication and discuss personal treatment questions with a clinician.
For a separate estimate of resting and daily maintenance energy, see the RMR and TDEE calculator. BMI alone does not determine energy needs or a weight-loss target.
Frequently asked questions
Can a healthy-range BMI miss a high waist measurement?
Yes. BMI is not a direct measure of where body fat is stored. Compare waist measurements and relevant health findings with a clinician when concerned.
Does a BMI of 25 automatically qualify me for weight-loss medicine?
No. Eligibility depends on the product’s local label, health conditions and a clinical review. BMI by itself cannot prescribe a treatment.
Sources and editorial note
CDC: Adult BMI Categories · WHO: Obesity and overweight · NICE: BMI and waist-to-height ratio · NHS: Pregnancy and adult BMI limitations · NHS hospital: Fluid changes and amputations in weight assessment. Sources and examples checked by Life Choice Note, 26 September 2026. This is general education and has not been independently physician-reviewed. It is not an individual diagnosis or prescription. Editorial standards · Disclaimer